Excess Quantum Research Articles

Gapless hinge states from adiabatic pumping of axion coupling

We demonstrate that chiral hinge modes naturally emerge in insulating crystals undergoing a slow cyclic evolution that changes the Chern-Simons axion angle $\theta$ by $2\pi$. This happens when the surface (not just the bulk) returns to its initial state at the end of the cycle, in which case it must pass through a metallic state to dispose of the excess quantum of surface anomalous Hall conductivity pumped from the bulk. If two adjacent surfaces become metallic at different points along the cycle, there is an interval in which they are in topologically distinct insulating states, with chiral modes propagating along the connecting hinge. We illustrate these ideas for a tight-binding model consisting of coupled layers of the Haldane model with alternating parameters. The surface topology is determined in a slab geometry using two different markers, surface anomalous Hall conductivity and surface-localized charge pumping (flow of surface-localized Wannier bands), and we find that both correctly predict the appearance of gapless hinge modes in a rod geometry. When viewing the axion pump as a four-dimensional (4D) crystal with one synthetic dimension, the hinge modes trace Fermi arcs in the Brillouin zone of the 2D hinge connecting a pair of 3D surfaces of the 4D crystal.

Enhancement of the Signal-to-Noise Ratio of an Atomic Magnetometer by 10 dB

Nonlinear magneto-optical rotation (NMOR) is a sensitive technique for measuring magnetic fields, though the polarization self-rotation (PSR) effect is a fundamental source of excess quantum noise that limits its sensitivity. This study uses a phase shifter to solve the limitation due to the PSR effect. Implementation of the phase shifter improves the signal-to-noise ratio up to 10 dB in the range of Earth's magnetic field. This approach should be useful for high-sensitivity magnetic field measurements in a geomagnetic environment.

In vivo cation exchange in quantum dots for tumor-specific imaging

In vivo tumor imaging with nanoprobes suffers from poor tumor specificity. Here, we introduce a nanosystem, which allows selective background quenching to gain exceptionally tumor-specific signals. The system uses near-infrared quantum dots and a membrane-impermeable etchant, which serves as a cation donor. The etchant rapidly quenches the quantum dots through cation exchange (ionic etching), and facilitates renal clearance of metal ions released from the quantum dots. The quantum dots are intravenously delivered into orthotopic breast and pancreas tumors in mice by using the tumor-penetrating iRGD peptide. Subsequent etching quenches excess quantum dots, leaving a highly tumor-specific signal provided by the intact quantum dots remaining in the extravascular tumor cells and fibroblasts. No toxicity is noted. The system also facilitates the detection of peritoneal tumors with high specificity upon intraperitoneal tumor targeting and selective etching of excess untargeted quantum dots. In vivo cation exchange may be a promising strategy to enhance specificity of tumor imaging.

The electronic factor in the act of adsorption of ions on a metal surface

The physical mechanism of the electron contribution to the electrochemical potential (intrinsic energy) of ions adsorbed on a metal surface is studied. The problem is reduced to consideration of the single-electron binding state in the fields of two attractors. For the bond between the anion and metal, the attraction centers are the potential of the atomic core of the anion and the potential reflecting the effects of interaction of the excess quantum charge with plasma degrees of freedom of the metal and formation of a surface axial plasmaron. On the average, the above attractors are neutral and are characterized by a finite range of action. The intrinsic energy of the cation of the metal surface depends on the energy of the valence electron in Coulombic fields of the cation itself, on the potential of the surface axial plasmahole, and on the energy of the mutual Coulombic repulsion of the above electron-attraction centers. Expressions are proposed for electronbinding terms of ions with a metal point by analogy with the mechanisms of formation of chemical σ- and π-bonds with partial charge transfer in molecular compounds.

Excess optical quantum noise in atomic sensors

Enhanced nonlinear optical response of a coherent atomic medium is the basis for many atomic sensors, and their performance is ultimately limited by the quantum fluctuations of the optical read-out. Here we demonstrate that off-resonant interactions can significantly modify the quantum noise of the optical field, even when their effect on the mean signal is negligible. We illustrate this concept by using an atomic magnetometer based on the nonlinear Faraday effect: the rotation of the light polarization is mainly determined by the resonant light-induced spin alignment, which alone does not change the photon statistics of the optical probe. Yet, we found that the minimum noise of output polarization rotation measurements is above the expected shot noise limit. This excess quantum noise is due to off-resonant coupling and grows with atomic density. We also show that the detection scheme can be modified to reduce the measured quantum noise (even below the shot-noise limit) but only at the expense of the reduced rotational sensitivity. These results show the existence of previously unnoticed factors in fundamental limitations in atomic magnetometry and could have impacts in many other atom-light based precision measurements.

A Combination of Spatial and Recursive Temporal Filtering for Noise Reduction when Using Region of Interest (ROI) Fluoroscopy for Patient Dose Reduction in Image Guided Vascular Interventions with Significant Anatomical Motion.

Because x-ray based image-guided vascular interventions are minimally invasive they are currently the most preferred method of treating disorders such as stroke, arterial stenosis, and aneurysms; however, the x-ray exposure to the patient during long image-guided interventional procedures could cause harmful effects such as cancer in the long run and even tissue damage in the short term. ROI fluoroscopy reduces patient dose by differentially attenuating the incident x-rays outside the region-of-interest. To reduce the noise in the dose-reduced regions previously recursive temporal filtering was successfully demonstrated for neurovascular interventions. However, in cardiac interventions, anatomical motion is significant and excessive recursive filtering could cause blur. In this work the effects of three noise-reduction schemes, including recursive temporal filtering, spatial mean filtering, and a combination of spatial and recursive temporal filtering, were investigated in a simulated ROI dose-reduced cardiac intervention. First a model to simulate the aortic arch and its movement was built. A coronary stent was used to simulate a bio-prosthetic valve used in TAVR procedures and was deployed under dose-reduced ROI fluoroscopy during the simulated heart motion. The images were then retrospectively processed for noise reduction in the periphery, using recursive temporal filtering, spatial filtering and a combination of both. Quantitative metrics for all three noise reduction schemes are calculated and are presented as results. From these it can be concluded that with significant anatomical motion, a combination of spatial and recursive temporal filtering scheme is best suited for reducing the excess quantum noise in the periphery. This new noise-reduction technique in combination with ROI fluoroscopy has the potential for substantial patient-dose savings in cardiac interventions.

Composition-dependent association behavior in the mixture of isopropanol and trichloromethane: a volumetric, vibration spectroscopic and quantum chemical study

Herein the intermolecular associative behaviors in the binary mixture of isopropanol and trichloromethane have been studied via a combined excess volumetric, vibration spectroscopic and quantum chemical approach.

Terahertz detectors based on superconducting hot electron bolometers

Low noise terahertz (THz) heterodyne detectors based on superconducting niobium nitride (NbN) hot electron bolometers (HEBs) have been studied. The HEB consists of a planar antenna and an NbN bridge connecting across the antennas inner terminals on a high-resistivity Si substrate. The double sideband noise temperatures at 4.2 K without corrections have been characterized from 0.65 to 3.1 THz. The excess quantum noise factor β of about 4 has been obtained, which agrees well with the calculated value. Allan variance of the HEB has been measured, and Allan time up to 20 s is obtained using a microwave feedback method. Also, the intermediate frequency gain bandwidth (GBW) was measured using two different methods, resulting in same GBW value of about 3.5 GHz.

Low Noise Receivers Based on Superconducting Niobium Nitride Hot Electron Bolometer Mixers from 0.65 to 3.1 Terahertz

SUMMARY Low noise terahertz (THz) receivers based on superconducting niobium nitride (NbN) hot electron bolometer (HEB) mixers have been designed, fabricated and measured for applications in astronomy and cosmology. The NbN HEB mixer consists of a planar antenna and an NbN bridge connecting across the antenna’s inner terminals on a high-resistivity Si substrate. To eliminate the influence of direct detection and instability of the local oscillation (LO) power, a wire grid has been used to change the input LO power for compensating the shift of bias current during Y-factor measurement. The double sideband (DSB) receiver noise temperatures at 4.2 K without corrections have been measured from 0.65 to 3.1 THz. The excess quantum noise factor β of about 4 has been obtained, which agrees well with the calculated value. Allan variance of the HEB has been characterized, and Allan time TA longer than 0.4 s is obtained. We also estimated the temperature resolution of the HEB from the Allan variance and obtained the minimum temperature resolution of 1.1 K using a Gunn oscillator with its multipliers at 0.65 THz as an LO source.

Excess quantum noise due to mode nonorthogonality in dielectric microresonators

This work presents a theory of the frequency-resolved light emission of active two-dimensional dielectric microresonators, which are characterized by a highly nonparaxial mode structure and frequently feature a position-dependent dielectric constant and nonuniform gain. The Lorentzian intensity profile is characterized by an appropriately generalized Petermann factor, a renormalized peak position, and the cold-cavity resonance lifetime $\ensuremath{\Gamma}$. The theory also delivers a relation of $\ensuremath{\Gamma}$ to the laser threshold that improves earlier phenomenological expressions even for the case of a homogeneous medium.

Excess noise reduction by optical technique in amplitude-sensitive heterodyne interferometer for small differential phase detection

An amplitude-sensitive technique associated with a heterodyne interferometer for detecting small differential phase is reported. The excess noise with the amplitude-sensitive technique is reduced by optical subtraction instead of electronic subtraction. The differential phase introduced by the orthogonally polarized laser beams is converted to the amplitudes of two heterodyne interferometric signals, which presents amplitude and phase quadrature simultaneously. Thus the excess noise power and quantum noise power are both differential phase dependent. The advantages of differential and additive operations by optical technique and the real time differential phase determination without phase lock in are demonstrated experimentally. The theoretical signal-to-noise ratio (SNR) and minimum detectable differential phase are derived, which takes quantum noise and excess noise into consideration. The experimental results demonstrated the resolutions of differential phase detection closes to 10(-6) rad/square root(Hz) (10(-13) m/square root(Hz)) level over 100 kHz bandwidth and at 10(-8) rad/square root(Hz) (10(-15) m/square root(Hz)) level over 125 MHz bandwidth, respectively, under 2.5 mW incident power.

The nature of a floating electron

Dynamics of electron solvation at the water surface is studied using extensive ab initio simulations. Calculations have been performed on semi-classical water at 300 K temperature with an excess quantum electron on its surface. It is found that after a very fast 30–50 fs initial localization, there follow fast 50–70 fs rotationally mediated transitions of the excess electron between surface trap states with a lifetime of 150–400 fs. In less then 2 ps the excess electron gets trapped in an ordered “floating” electron state on the surface of water with a lifetime of more than 7 ps. The excess electron diffusion coefficient and spectrum of its velocity autocorrelation function change over time to reflect a transition from a very mobile phase (first 2 ps) to a trapped “floating” electron phase (2–7 ps).

Resonant excess quantum noise in lasers with mixed guiding.

We show experimentally that the combination of soft-edged gain and index guiding can lead to resonant excess quantum noise. Resonances with excess noise factors close to 100 are observed in end-pumped Nd3+:YVO4 lasers for cavity lengths in which two modes experience similar gain. An associated increase in the relaxation oscillation damping rate demonstrates that the fluctuation enhancement is indeed caused by excess quantum noise and not by dynamic instabilities.

Subthreshold optical parametric oscillator with nonorthogonal polarization eigenmodes

We study the behavior of a type-II degenerate parametric amplifier in a cavity with nonorthogonal polarization eigenmodes. The mode nonorthogonality is achieved by introducing circular birefringence and linear dichroism. We use a scattering matrix formalism to investigate the role of excess quantum noise in such a device. Since only two modes are involved we are able to derive an analytical expression for the twin-photon generation rate measured outside the cavity as a function of the degree of mode nonorthogonality. Contrary to recent claims we conclude that there is no evidence of excess quantum noise for a parametric amplifier working so far below threshold that spontaneous processes dominate. Using the same scattering matrix formalism we also investigate the output spectrum of the amplifier near the threshold of parametric oscillation. We find optical band structures very similar to those known for passive ring cavities. These optical band structures are studied as a function of mode nonorthogonality and mirror reflectivity.

Does excess quantum noise exist in spontaneous processes?

We investigate the role of excess quantum noise in type-II degenerate parametric down-conversion in a cavity with non-orthogonal polarization eigenmodes. Since only two modes are involved we are able to derive an analytical expression for the twin-photon generation rate measured outside the cavity as a function of the degree of mode non-orthogonality. Contrary to recent claims we conclude that there is no evidence of excess quantum noise for a parametric amplifier working so far below threshold that spontaneous processes dominate.

Solvation dynamics following electron photodetachment from I− in aqueous clusters

Equilibrium and dynamical aspects of the earliest stages of solvation following the electronic excitation of I− dissolved in aqueous clusters were investigated, using a mixed quantum-classical molecular dynamics algorithm. The systems were modeled as composed by an excess quantum charge coupled to a classical bath that includes a neutral iodine and Nw=6, 50, and 100 water molecules. In small clusters, the equilibrium solvation structures of the iodine are characterized by surface states that gradually turn into interior states as one considers larger aggregates. Electronic properties of the ground and first excited states are described. In small aggregates, both states are characterized by highly diffuse density profiles that extend well beyond the spatial extent of the aggregates. In larger clusters, the confining potential provided by the classical bath localizes the electron within the aggregates. Dynamical aspects of the solvation relaxation following a vertical excitation of the solute were also examined. In all cases, the relaxation mechanisms involve a global reorganization of the original solvation structure characterized by a gradual stabilization of the solvent-solvent interactions in detriment of a less favorable electron solvation. The overall characteristic time for the solvation is in the order of τs≈0.05 ps for Nw=6 and attains τs≈0.60 ps for Nw=100.

Threshold behavior of a laser with nonorthogonal polarization modes

We investigate experimentally and theoretically the influence of the excess quantum noise in a laser on the laser’s input‐output curve near threshold. As an experimental system we use a He‐Xe gas laser with nonorthogonal polarization modes. We observe that the excess quantum noise is absent far below threshold and steadily builds up as threshold is approached. The excess noise is fully developed when the mode that (above threshold) becomes the lasing mode dominates in power the other, nonlasing, modes. This situation may already occur considerably below threshold, namely, when the hot-cavity photon lifetime of the dominant mode exceeds the coloring time of the excess noise. © 2002 Optical Society of America OCIS codes: 270.2500, 270.3430.

Two-Frequency Lasers: from Excess Quantum Noise to RF Photonics Applications

We illustrate the physics of two-frequency lasers by two examples. The first example illustrates the fundamental consequences of the existence of two eigenstates on the laser line width. We indeed show experimentally thatthe non-orthogonality of these two eigenstates results in an increase in the laser quantum noise. We also give a physical explanation of this vectorial excess noise factor. The second example illustrates the capabilities of two-frequency lasers in terms of applications. In the domain of RF frequency generation by optical means, we show how a pulsed two-frequency source can be built for lidar-radar applications and pulsed RF frequency generation.

Low quantum noise laser diodes

It is demonstrated that laser diodes can be optimised for low quantum noise operation. Attention is given to the excess quantum noise arising due to non-orthogonal longitudinal modes in laser diodes with asymmetric facet reflectivities. It is shown that in symmetric high-reflectance faceted laser diodes such excess noise is eliminated, and thus this is a good design option for low quantum noise devices. It is further shown how the threshold current/quantum efficiency ratio of this structure may be optimised. This shows the importance of knowing the internal loss and facet reflectances, and then using an appropriate device length. The superior spectral purity of these devices is also indicated. Such devices are recommended for investigating sub-Poissonian light, using quiet pump sources. Squeezed light generation may be possible using asymmetric high-reflectance devices (∼70–100%), with less asymmetry than is normally used (∼10–90%).

Excess noise factor in circular grating distributed Bragg reflector lasers

In this paper, the excess quantum noise in circular grating distributed Bragg reflector (CG-DBR) lasers is analyzed taking the effect of mode non-orthogonality into account. An expression for the excess noise factor is derived. Numerical results obtained for CG-DBR laser reveal that real parameters of the laser structure have a remarkable effect on the level of excess quantum noise.